1. Field of the Invention
The present invention relates generally to oil resistant silicone compositions. More particularly, the present invention relates to oil resistant condensation curing silicone compositions which are suitable for sealing and gasketing applications. Methods of making and using such condensation curing silicone compositions are also provided.
2. Brief Description of Related Technology
Conventional room temperature vulcanizable (xe2x80x9cRTVxe2x80x9d) silicone compositions have excellent sealing and adhesive properties. Such compositions can be formed into gaskets which are used extensively in the automotive industry. For example, several patents assigned to Loctite Corporation and set forth in more detail below, disclose various oil resistant silicone sealant compositions.
In particular, U.S. Pat. No. 4,514,529 (Beers) generally discloses a low modulus, high elongation RTV silicone composition having oil resistance. This composition may include a devolatilized silanol-terminated diorganosiloxane of 2,000 to 250,000 Cst, a devolatilized diorganosiloxane fluid plasticizer terminated with triorganosiloxy groups, a cross-linking agent, a catalyst and a filler. Articles formed from such a composition can be used as, e.g., gasket sealants, as well as formed-in-place gaskets for use on internal combustion engines.
U.S. Pat. No. 4,673,750 (Beers), U.S. Pat. No. 4,735,979 (Beers) and U.S. Pat. No. 4,847,396 (Beers) generally disclose adhesion promoter compositions for use in auto-adhering, one-component RTV silicone sealant systems having oil resistance. The adhesion promoters set forth in these patents include glycidoxyalkyl substituted mixed alkoxy-oxime silanes and di-substituted mixed oxime-alkoxysilylalkyl ureas, respectively. The RTV silicone compositions which contain these oxime adhesion promoters generally include polydimethylsiloxanes, trimethylsilyl terminated polydimethylsiloxanes and various other fillers, additives and catalysts. Such compositions may be used to, e.g., make formed-in-place gasket materials.
International PCT Publication No. WO 93/19130 discloses a one-part RTV silicone rubber composition as a formed-in-place gasket having oil resistant properties. Such a composition includes a diorganopolysiloxane, a M-stopped plasticizer, such as for example, R3xe2x80x94Sixe2x80x94(OSiR2)xxe2x80x94OSixe2x80x94R3, gamma-aminopropyltriethoxysilane, a catalyst, a crosslinker and various fillers. M-stopped silicone plasticizers are generally trimethyl terminated non-reactive silicone compositions. The compositions disclosed by this International patent publication are reported to have oil resistance and good adhesive properties and are especially adapted for use in the automobile industry.
As might be expected for gasketing articles and adhesives used in the automobile industry, such as engine seals and gaskets, retention of adhesion and maximization of joint movement after oil immersion at elevated temperatures is highly desirable. Silicone plasticizers are conventionally used to modify silicone gasketing compounds, such as for example, to lower the modulus of the composition and improve joint movement and the extrudability of the finished product. All of the RTV silicone adhesive compositions set forth above contain M-stopped silicone plasticizers for accomplishing such goals.
It would be desirable to provide such silicone adhesive compositions without using M-stopped plasticizers
The present invention provides a silicone composition, which includes a silanol terminated silicone fluid, an organic plasticizer, a filler and a crosslinker. The reaction product of this composition forms an oil resistant adhesive silicone composition.
The invention also provides a method of applying a silicone composition to a surface exposed to oil during its intended use. This method includes applying to the exposed surface a composition that includes a condensation curing silanol terminated silicone polymer, an organic plasticizer, a filler and a crosslinker. The method further includes forming the composition into an appropriate sealing configuration and allowing the composition to cure at room temperature into an oil resistant silicone adhesive.
Also, the invention provides a method of using an oil resistant mechanical seal, which remains adhesive after exposure to oil. This method includes applying a seal forming amount of a composition on a surface of a mechanical part. The composition is formed from a condensation curing silanol terminated silicone polymer, an organic plasticizer, a filler and a crosslinker. The method further includes forming a seal between at least two mechanical surfaces by room temperature vulcanization, wherein the seal remains competent when exposed to oil.
Still further, the invention provides a method of using an oil resistant sealing member that remains adhesive after immersion in oil. This method includes forming a seal between two or more surfaces by applying therebetween the oil resistant sealing member formed from a composition that includes a condensation curing silanol terminated silicone polymer, an organic plasticizer, a filler and a catalyst.
It has been found surprisingly that by substituting such M-stopped silicone plasticizers with organic plasticizers in these RTV silicone systems that compositions are formed with significantly improved adhesive properties and resistance to oil.
The present invention will be more fully understood by a reading of the section entitled xe2x80x9cDetailed Description of the Inventionxe2x80x9d.
The present invention is directed to condensation curing silicones having improved adhesive properties when exposed to oil. Conventional RTV silicones having M-stopped silicone plasticizers, however, are less desirable for adhesives and articles that are exposed to high temperature oils, such as for example, engine O-rings and gaskets typically used in the automotive industry. Surprisingly, as noted above, it has been found that by substituting an organic plasticizer for the M-stopped silicone plasticizer in such RTV silicone compositions that improved adhesive and oil resistance is obtained.
The present invention provides a silicone composition that includes a silanol-terminated silicone fluid, an organic plasticizer for maintaining adhesion of the composition after exposure and/or immersion in oil, a filler and a crosslinker. The reaction product of this composition is an oil resistant adhesive.
As used herein, xe2x80x9csilanol terminated silicone fluidxe2x80x9d includes room temperature condensation curing silicone polymers. Such polymers are conventional silicone polymers that are able to cure/vulcanize using moisture from the air at ambient temperature (approximately 25xc2x0 C.). Higher curing temperatures, however, can also be used, such as for example 50xc2x0 C., so long as the oil resistant and adhesive properties of the cured elastomers are not compromised.
The silicone polymers of the present invention typically contain functional groups capable of reacting with moisture to substantially cure the composition. Typically, such condensation curing silicone polymers include, for example, polydiorganosiloxanes having terminal hydroxyl groups that are curable to an elastomer upon cross linking. Other silicone compositions, however, can be used in the present invention so long as they are capable of condensation curing to form the oil resistant silicone compositions as described in more detail below.
In the present invention, these silicone polymers can have viscosities that range from about 2,000 Cst to about 200,000 Cst. Desirably, these polymers can range in viscosity from about 4,000 Cst to about 50,000 Cst. Viscosity ranges for these polymers of from about 6,000 Cst to about 20,000 Cst can also be used in the present invention.
The adhesive silicone compositions of the present invention also include one or more organic plasticizers. As used herein, xe2x80x9corganic plasticizerxe2x80x9d refers to carbon atom-containing plasticizers that do not contain silicone atoms. Any conventional organic plasticizer able to form the present fuel resistant silicone compositions can be used in the present invention. For example, suitable organic plasticizers that can be used in conjunction with the present invention include aliphatic liquid polymers and oils. Other organic plasticizers that can be used in the present invention include, for example, petroleum derived organic oils. Moreover, other suitable organic plasticizers include, for example, alkyl phosphates, polyalkylene glycol, poly(propylene oxides), hydroxyethylated alkyl phenol, dialkyldithiophosphonate, poly(isobutylenes), poly(xcex1-olefins) and mixtures thereof. Desirably, the plasticizer is a liquid polyisobutylene or other similar composition.
In the present compositions, effective amounts of organic plasticizers are added to ensure the desired workability and oil resistance of the final elastomer. Accordingly, from about 1% to about 50% by weight of a selected organic plasticizer can be incorporated into the compositions of the present invention. Desirably, from about 10% to about 36% by weight of a selected organic plasticizer, such as about 14% to about 25%, can be incorporated into the compositions of the present invention.
As shown in the examples below, the use of organic plasticizers in place of M-stopped silicone plasticizers significantly increases the shear adhesion and joint movement of the compositions of the present invention because the organic plasticizers do not significantly equilibrate into the cured polymer matrix. Thus, the present compositions have significantly improved adhesion and oil resistant properties compared to conventional RTV silicone compositions having M-stopped silicone plasticizers.
The silicone compositions of the present invention also contain fillers depending upon the desired properties and functions of the final cured elastomer. These fillers include, for example, titanium dioxide, lithopone, zinc oxides, zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, calcium carbonate, fumed silica, precipitated silica, glass fibers, magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, crush cores, calcium clay, carbon, graphite, cork, cotton, synthetic fibers and mixtures thereof. Other conventional fillers can also be incorporated into the present compositions provided they do not adversely effect the oil resistant and adhesive properties of the final end product produced therefrom.
The silicone compositions of the present invention also include one or more crosslinkers. In the present invention, the crosslinker includes, for example, methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltriacetoxysilane, vinyltriethoxysilane, methyltriacetoxysilane, methyl tris-(N-methylbenzamido)silane, methyl tris-(isopropenoxy)silane, methyl tris (cyclohexylamino)silane, methyl tris-(methyl ethyl ketoximino)silane, vinyl tris-(methyl ethyl ketoximino)silane, methyl tris-(methyl isobutyl ketoximino)silane, vinyl tris-(methyl isobutyl ketoximino)silane, tetrakis-(methyl ethyl ketoximino)silane, tetrakis-(methyl isobutyl ketoximino)silane, tetrakis-(methyl amyl ketoximino)silane, dimethyl bis-(methyl ethylketoximino) silane, methyl vinyl bis-(methyl ethyl ketoximino)silane, methyl vinyl bis-(methyl isobutyl ketoximino)silane, methyl vinyl bis-(methyl amyl ketoximino)silane, tetrafunctional alkoxy-ketoxime silanes, tetrafunctional alkoxy-ketoximino silanes and enoxysilanes. Other conventionally known crosslinkers can also be used with the present compositions, provided they are able to crosslink the present compositions without adversely affecting the adhesive and oil resistant properties of the final elastomeric articles formed therefrom.
The present silicone compositions can also include optional catalysts for increasing the cure rate thereof. Any conventional catalyst system may be employed with the present compositions provided the excellent adhesive and oil resistant properties of the final elastomeric articles are not compromised. Suitable catalysts that can be used with the present compositions, include for example, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin maleate, dialkyl tin hexoate, dioctyltin dilaurate, iron octanoate, zinc octanoate, lead octanoate, cobalt naphthenate, tetrapropyltitanate, tetrabutyltitanate, tin dimethyl bis neodecanoate, dialkyl tin carboxylates, mercaptans and titanates.
Other additional additives can also be incorporated into the present compositions, provided they do not adversely effect the ability of these compositions to resist certain organic solvents, such as oil, and to maintain their excellent adhesive properties. For example, an adhesion promoter can be added to the present compositions. Such an adhesion promoter can include, for example, gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, trimethoxysilylpropyldiethylene triamine, 3-glycidoxypropyltrimethoxy silane, gamma-mercaptopropyltrimethoxysilane and gamma-methacryloxypropyltrimethoxysilane.
Conventional pigments, such as for example, titanium dioxide pigment, can also be incorporated into the present invention provided they do not adversely effect the oil resistant and adhesive properties of the final end product produced therefrom.
The reaction products of present compositions are useful as adhesives for bonding together surfaces that are exposed to oil during their intended use. Thus, the present adhesive compositions can be used on oil exposed surfaces in, for example, conventional 2 cycle engines. The compositions of the present invention may also be formed into many different configurations and then condensation cured over time under ambient or elevated temperature conditions. Articles formed in such a manner are useful in various industries where there is a need for oil and/or fuel resistant silicone-based elastomeric articles. In the automotive industry, for example, O-rings, hoses, seals, and gaskets can be formed from the present compositions. Other conventional uses requiring good adhesive properties, as well as fuel and/or oil resistance are also contemplated for the present compositions.
In another embodiment of the present invention, there is provided a method of applying a silicone composition to a surface exposed to oil during its intended use. The surface to which the present compositions are applied can be any work surface that is exposed to oil and/or fuel, such as certain work surfaces of conventional internal combustion engines. This method includes applying a composition of the present invention to the work surface.
Briefly, this composition includes a condensation curing silanol terminated silicone polymer, an effective amount of an organic plasticizer to maintain adhesion of the composition after immersion in oil, a filler and a crosslinker. The composition is subsequently formed into an appropriate sealing configuration and then allowed to cure at room temperature to form an oil resistant silicone adhesive.
In yet another embodiment of the present invention, there is provided a method of using an oil resistant mechanical seal which remains adhesive after exposure to oil. This method includes applying a seal forming amount of the composition as described previously onto a surface of a mechanical part. This composition is formed from a condensation curing silanol terminated silicone polymer, an effective amount of an organic plasticizer to maintain adhesion of the composition after immersion in oil, a filler and a crosslinker. A seal is then formed between at least two mechanical surfaces by, for example, room temperature vulcanization, wherein the seal remains competent when exposed to oil.
In still yet another embodiment of the present invention, there is provided a method of using an oil resistant sealing member that remains adhesive after contact with and/or immersion in oil. This method includes forming a seal between two or more surfaces by applying therebetween the oil resistant sealing member formed from a composition according to the present invention.
In each of the methods set forth above, the compositions may be formed into any conventional article useful for creating seals around or between work surfaces, such as for example, O-rings and gaskets.
The following examples are provided to further illustrate methods of preparation of the silicone compositions, and used elastomers thereof, as well as certain physical properties of these materials, These examples are illustrative only and are not intended to limit the scope of the invention in any way.